The invention primarily relates to the removal of impurities such as CO.sub.2 from breathable atmospheres within a confined area. Various chemical and particulate filtration prior art systems are used for purification of gas mixtures. Such systems are particularly useful in confined areas such as aircraft cabins, spacecraft cabins, and submarines where sufficient fresh clean air is not available from the surrounding environment or otherwise impractical to obtain by other means.
U.S. Pat. No. 3,891,411 to Meyer discloses a purification system using zeolite molecular sieve beds. This invention discloses two beds which are configured in a parallel relationship and through which a gas is passed in order to remove the carbon dioxide therefrom. A system of valves controls the pressure of the gas passing through each of the beds. In order to adsorb carbon dioxide from the gas to be purified, the gas must be pressurized. Conversely, in order to remove this carbon dioxide from the desorbing bed and to thereby regenerate this bed, the gas passing therethrough must be at a relatively low pressure. Thus, this prior art system depends on a pressure swing between the desorbing and adsorbing beds. However, since additional energy must be expended in order to pressurize and depressurize the gas mixture passing through the beds, this prior art system is not energy efficient. Thus, the system may not be as desirable in applications where energy efficiency is required because of fuel constraints.
Still another prior art system incorporates a carbon molecular sieve for adsorption of CO.sub.2. A representative example of such a prior art system is U.S. Pat. No. 3,729,902 to Ventriglio. This patent discloses an activated carbon sieve on which the chemical K.sub.2 CO.sub.3 is distributed. However, this zeolite molecular sieve system shows an affinity for H.sub.2 O as well as CO.sub.2. Liquid water adsorption by the zeolite beds will severely reduce their ability to adsorb CO.sub.2 or other gases and therefore water must be removed prior to reaching the zeolite bed by addition of a dessicant device or the air heated to a level sufficient to reduce the water to vapor. Thus, in some applications where a dessicant is used, the water must be added back into the system by means of a humidifier. Addition of the dessicant, humidifier and water ducting is a severe penalty for airborne systems where a lightweight system is essential. Moreover, this prior art system also uses heated air to promote the adsorption of CO.sub.2. This heated adsorption air is at a relatively high temperature and the desorption air is required to be at a still higher temperature in order to regenerate the zeolite sieve bed. Consequently, a disadvantage with such prior art systems is that they have a high energy cost due to the requirement of heating the air to the extreme temperatures required, and also have the added complexity, weight and energy cost involved in adding water back into the air which has been purified.
Other prior art systems recuperate the heat utilized in desorption of the bed. An example of such a prior art system is in U.S. Pat. No. 4,472,178 to Kumar. This prior art system is specifically designed for use in cryogenic adsorption systems. Such systems particularly remove water as well as carbon dioxide from the air stream. This system discloses a heat recuperator, specifically an accumulator is used as a heat recuperator to remove the heat from the air after the air has been adsorbed and transmit it to the desorption air stream in order to conserve heat energy and thereby reduce energy requirements of the system. However, the use of an accumulator to conserve energy may not be practical in many applications, particularly those on which space and weight are limited.
An air purification system is thus needed which is hydrophobic and which is capable of adsorbing CO.sub.2 at normally available supply air pressures. Moreover, an air purification system is also needed that can remove the CO.sub.2 with low energy consumption and minimal weight and size penalty.